Due to a variety of medical conditions, intrinsic cardiac depolarization may diminish in its ability to cause a coordinated mechanical contraction of the heart sufficient to provide adequate blood flow from the heart. These medical conditions may include dysfunctions of the sinus node, atrioventricular node, or the electrical conduction pathways in the heart, e.g., the Bundle of His and Purkinje fibers. When cardiac output is limited due to such a dysfunction, a patient may turn to medical intervention to alleviate the problem and restore normal cardiac function.
Commonly, such dysfunctions may be treated with an artificial pacemaker that regulates the function of the heart. An artificial pacemaker is a medical device that generates and delivers electrical impulses to the patient's heart to regulate the contraction of cardiac muscle. The electrical impulses are generally delivered to one or more locations within the heart to effectively depolarize the cardiac muscle. In this manner, the pacemaker manages the timing of atrial and ventricular contraction to adequately pump blood throughout the systemic and pulmonary vasculature.
In some patients, one or more areas of the cardiac muscle have been damaged due to ischemia caused by coronary artery disease that prevented adequate blood flow to the cardiac tissue. Such damaged areas are referred to as myocardial infarctions. Infarct tissue does not contract when stimulated in the same manner as healthy cardiac muscle does. Instead, the infarct tissue expands and thins while the rest of the heart is thickening during each cardiac cycle. Non-uniform contraction of cardiac muscle can lead to infarct expansion and overall remodeling of the heart. Remodeling of the heart can lead to cardiac muscle dysfunction, cardiac conduction dysfunction, decreased cardiac output and, eventually, heart failure.